92 PROCEEDINGS OF THE AMERICAN ACADEMY 



heavy material, and not of Lemna leaves nor Plumatella eggs. It 

 would seem, then, that when its tube is heavy the animal has the habit 

 of swallowing air-bubbles to keep it afloat. When driven from its 

 tube, it swims about like a water-snake, but immediately seeks cover. 

 Its food consists ol' diatoms and other unicellular Ali^a^ and small water 

 animals of every kind. 



The only method of reproduction that I have observed is that by 

 budding. No attempt has been made to determine the existence of a 

 numerical law governing the budding process. The phenomena do 

 not seem to differ from those described for related forms. In the 

 sixth and seventh segments rounded cell-masses have been seen, which 

 are probably the rudiments of the testes and ovaries, but they were 

 never sufficiently developed to allow a satisfactory study of them. 



Anatomy. 

 The Body Wall. 



The body wall consists of four layers, in the following order, from 

 without inward : a culicula, tlie matrix of the cuticula or dermis, an 

 annular muscular layer, and a loiigitudiuid muscular layer. 



The cuticula is a thin structureless membrane covering the entire 

 surface of the body. It is easily seen in all sections, and may be 

 demonstrated by leaving the animal for half an hour in a very weak 

 chromic acid solution, or by using a very weak solution of potassium 

 hydrate. Frequently, when the animal dies in water, the cuticula 

 becomes raised up into vesicular swellings and is thus rendered plainly 

 visible ; when some part of the animal, as a digitiform appendage, is 

 crushed, it then also shows plainly. The cuticula presents no mark- 

 ings under a power of six hundred diameters. 



The matrix of the cuticula, the dermis, consists in most regions of 

 a single layer of j)rismatic cells. The latter are, however, several 

 layers deep on the frontal lobe. This layer is thicker at the head and 

 tail ends, and in the region of the head and tail it is also thicker on 

 the ventral than on the dorsal side. Tlie dermal cells have large 

 granular nuclei, the walls of which are frequently more distinct than 

 those of the cells themselves. Each nucleus contains one or several 

 nucleoli. The cells and their nuclei are longer in the head and tail 

 regions than elsewhere. 



IMany unicellular dermal glands (PI. II. figs. 11,13, drm. gl) are found 

 in the region of tlu; head, especially on the frontal lobe, and a few in 

 the region of the [)avilion. These glands vary in sha{)e. Frequently 



